1. (Field of the Invention)
The present invention generally relates to an image forming apparatus employing an electrophotographic copying process and, more particularly, to an electrophotographic copying machine.
2. (Description of the Prior Art)
The electrophotographic copying machine is known to comprise a photosensitive medium supported for movement past a charging station at which an electrostatic charger is disposed for imparting an electrostatic charge to the photoreceptor medium; an exposure station at which a ribbon of light carrying an image of an original document to be copied is projected onto the photoreceptor medium to form an electrostatic latent image on the photoreceptor medium in a pattern complemental to the image of the original document; a developing station at which a developing system is disposed for applying toner material to the photoreceptor medium to develop the electrostatic latent image into a visible powder image; a transfer station at which the powder image can be transferred onto a copying paper supplied from a paper supply unit; a paper separating station at which the paper with the powder image having been transferred thereto is separated or removed away from the photoreceptor medium; and a cleaning station at which the residual toner material and the residual electrostatic charge both remaining on the photoreceptor medium are removed in readiness for the next cycle of electrophotographic copying process. The copying paper so separated or removed from the photoreceptor medium is transported to a fixing station at which the powder image on the copying paper is permanently fixed.
The electrophotographic copying machine having a plurality of developing units is also well known in the art. In this type of copying machine, toner material of different colors are accommodated in the respective developing units, and the developing units are adapted to be selectively driven into operation for applying the toner material in the selected developing unit to the photoreceptor medium to form the powder image.
In any event, at the separating station, either a mechanical separating pawl, a discharger for applying an alternating current to remove the charge built up on the copying paper for the purpose of lessening the force of attraction acting between the photoreceptor medium and the copying paper, of a combination thereof has hitherto been employed for separating the copying paper from the photoreceptor medium.
In the system wherein the mechanical separating pawl is employed, the tip of the separating pawl must be carefully designed and tailored to avoid any possible damage to the photoreceptor medium. Therefore, not only is the separating pawl supported for movement between separating and retracted positions either in a direction laterally of the direction of movement of the photoreceptor medium or in a direction close towards and away from the photoreceptor medium, a complicated and expensive mechanical system is necessitated for the support of the separating pawl.
On the other hand, in the system wherein the discharger is employed, the extent to which the copying paper with the visible powder image having been transferred thereto at the transfer station is smoothly separated away from the photoreceptor medium at the subsequent separating station tends to be affected by several conditions including, inter alia, the condition in which toner particles are applied to the photoreceptor medium and the charging condition of the photoreceptor drum. Accordingly, it has often been experienced that the copying paper with the powder image having been transferred thereto is carried away from the separating station together with the continued movement of the photoreceptor medium without being separated from the photoreceptor medium.